This application claims the priority of German Patent Application, Serial No. 101 53 704.2, filed Oct. 31, 2001, pursuant to 35 U.S.C. 119(a)(d), the disclosure of which is incorporated herein by reference.
The present invention relates, in general, to a plastics injection molding machine.
German Pat. NO. DE 41 20 403 C2 describes an injection molding machine having an injection mold which is heated and cooled alternately at timed intervals and constructed to use the waste heat from a machine drive to heat the injection mold. The injection mold should be heated as rapidly as possible to an elevated temperature level, which means that a heat source is required that is able to produce such heat in a very short period. On the other hand, the machine drive produces only a fairly even heat amount, independent on the heating and cooling cycles of the injection mold. In addition, this heat amount is insufficient for realizing a quick heating action of the injection mold. Thus, the use of waste heat is possible only to a limited extent, and the provision of an additional heat energy source is therefore required.
This conventional injection molding machine further describes the use of an air stream, which has been heated previously in a heat protection jacket of the plasticizing cylinder, for drying the plastic material in a granulate reservoir, upstream of the plasticizing cylinder. However, only a fraction of the heat amount to be supplied to the air stream can hereby be provided by the insulation losses of the heat protection jacket. The remaining part must be generated by an increased withdrawal of useful heat of the plasticizing cylinder, so that the energy saving aspect during the drying process is accompanied by a respective greater energy consumption during heating of the plasticizing cylinder.
It would therefore be desirable and advantageous to provide an improved injection molding machine to obviate prior art shortcomings and to significantly reduce the energy consumption.
According to one aspect of the present invention, a plastics injection molding machine, includes a heatable plasticizing cylinder having an inlet side for incoming plastic material and a machine drive, an injection mold receiving the plastic material from the plasticizing cylinder for making an injection molded article, and a heat transport system acting between the machine drive and the inlet side of the plasticizing cylinder for preheating the incoming plastic material with waste heat from the machine drive for recovery of energy.
The present invention resolves prior art problems by providing a heat transport system which directly and continuously preheats the plastic granulate on the inlet side of the plasticizing cylinder with waste heat of the machine, without need for a complicated intermediate reservoir or additional energy consumption, so as to realize an extremely effective waste heat exploitation. In this way, not only the heat energy consumption of the plasticizing cylinder, required for the melting process, can be significantly reduced but also the melting zone of the plasticizing cylinder can be shortened and the productivity of the plasticizing drive is significantly improved as a consequence of the resultant smaller pressure rise in the area of the melting zone.
According to another feature of the present invention, the machine drive may include a central electro-hydraulic motor and pump unit, wherein the heat transport system preheats the incoming plastic material with waste heat from the motor and pump unit.
According to another feature of the present invention, the machine drive may include a screw drive secured at the inlet side of the plasticizing cylinder, wherein the heat transport-system is linked in a heat-absorbing manner to the screw drive at an attachment zone to the plasticizing cylinder. In this way, the waste heat use is further improved and the screw drive is effectively protected from overheating.
According to another feature of the present invention, there is provided a feed hopper at the inlet side of the plasticizing cylinder, whereby the plastic material is preheated in the feed hopper. This configuration is especially easy to implement.
According to another feature of the present invention, the heat transport system may be a pipe system circulated by water in a closed circuit. This configuration is easy to implement and is thermally effective.